The new poll suggested that Warren’s argument that a Brown victory could put Republicans in control of the Senate may be resonating with voters. According to the poll, 52 percent of Massachusetts voters want Democrats in control of the Senate, compared with 35 percent who want to see the GOP in the majority.

The poll also found that both Brown and Warren have seen their popularity dip amid a barrage of negative ads. About 49 percent of voters have a favorable opinion of Brown, compared with 42 percent who hold an unfavorable opinion, a drop from the firm’s last poll in mid-September that found the senator with a 55 percent to 35 percent favorability rating.

Warren has a 49 percent to 45 percent favorability rating, down from 51 percent and 43 percent in the September poll.

In the presidential race, President Obama leads Mitt Romney in Massachusetts, though by the smallest margin this year, suggesting Obama has suffered a post-debate slump in this Democratic bastion, just as he has nationally.

The poll found 55 percent of Massachusetts voters support Obama, compared with 41 percent who favor Romney, the state’s former governor who has based his campaign in Boston. Obama held an 18-point lead in the September poll.

The poll also found that Massachusetts voters are inclined to legalize assisted suicide and medical marijuana by approving two controversial ballot questions in November.

About 56 percent of voters support the assisted suicide referendum, compared with 30 percent who oppose the measure. Voters back the medical marijuana question by 57 percent to 31 percent.

Public Policy Polling used automated telephone calls to survey 1,051 likely Massachusetts voters from Oct. 9 to Oct. 11. The poll has a margin of errror of plus or minus 3 percentage points.